Polyurethane/Polyisocyanurate foam (PIR/PUR boardstock) has been widely used to insulate roofs and walls of commercial and industrial buildings due to its excellent thermal insulation, flame resistance, and mechanical properties. The reason for its excellent flame resistance is formation of isocyanurate trimer during the foaming process. However, certain building insulation applications, such as air handling, require very stringent fire and smoke performance that even standard PIR/PUR boardstock cannot meet.